The invention relates to a computer interface unit for a measuring instrument such as an audiometer. Such instruments are known for instance from the British Pat. No. 1,599,367.
If such a measuring instrument is to be automatically controlled by a computer, all control processes, as for example the selection of volume or frequency response, must be electronically remote-controllable. In addition, provision must be made that the control lines, required in large number, can be operated successively by a few computer control lines, and that the selected functions remain set until changed. As is known, tasks such as these are performed by computer interfaces.
Known interfaces, are too complicated to be usable with each measuring module of instruments that are used in practice. In addition, known interfaces require signal sequences which extremely simple computers, such as are used in audiometry or hearing aids, cannot supply without additional hardware.
To construct a low-cost instrument for manual operation which can be easily adapted for automatic control by a computer, the modules to be operated--e.g., the sound generator, the volume control, etc., of an audiometer--must be controllable by simple manual switches. Such an arrangement is advantageous also in computer-controlled measuring instruments because, in case of error, the manual override of the computer by the manual switches makes it possible to determine which errors had previously been caused by the computer alone. Conventional interfaces are not fully suitable for this task, as their operation is too complicated.
Audiometers employed in the medical sector are continually subject to increased requirements for electrical safety. However, it is often required to connect the instruments to outside computer components, e.g., to central computers of a company which meets lower safety requirements. For this reason a d-c isolation must be provided for the higher stipulated differential voltage between the computer and the components to be controlled or between the computer and the outside computer components. The first solution is more favorable because it eliminates the disturbance of the sometimes extremely weak useful signals of the audiometer by the d-c coupling with the control signals of the computer.
Inexpensive coupling elements, such as optocouplers, for differential voltages over 4 kV, result in time differences of the control signals during parallel transmission as required for rapid control processes. Here the conventional interfaces require additional expenditure for reliable operation, e.g., in the form of delay compensating circuits.